Battery packs, such as Lithium-Ion (Li-Ion) battery packs experience a self discharge process when stored, even when not in use. Monitoring circuitry (such as an analog front end—bq29330 and/or a bq20z70, available from Texas Instruments) accelerates the discharge rate when powered by the pack cells. Preventative maintenance charging is needed to prolong battery shelf life when a monitoring gauge uses battery power to monitor a state of health of the cells during storage. Such preventative charging is costly.
To address the discharge issue when storing a battery pack, conventional battery storage systems use a number approaches such as (i) implementing a sleep mode command on the battery charger, (ii) providing a preventative maintenance program that periodically charges the packs, or (iii) configuring the design with a mechanical connection so that the battery packs are not connected to the charger when the packs are not installed.
Such systems have one or more disadvantages. The sleep command of a typical charger is not effective when implemented on a two pack system. A two pack configuration from an I2C switch of a typical charger is a passive switch command. Additionally, many of the systems configured with a battery pack will be shipped with the battery packs installed. Preventative maintenance charging needs to be reserved for field replacement units. The physical chassis on many designs are often set by the standard bridge bay (SBB) specification. The space for a battery back-up chassis is a predefined form factor. Such a form factor needs a design that maintains the predefined volumetric limitations.
It would be desirable to implement a battery backup system that fits in a predefined form factor and with an embedded charger implements a low power mode that allows two or more battery packs to remain in a usable state during storage.